This invention relates to a novel synthetic porous crystalline material, EMM-1, to a method for its preparation and to its use in catalytic conversion of organic compounds.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline metallosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities, which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as xe2x80x9cmolecular sievesxe2x80x9d and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO4 and Periodic Table Group IIIA element oxide, e.g., AlO4, in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total Group IIIA element and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing the Group IIIA element is balanced by the inclusion in the crystal of a cation, for example an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the Group IIIA element, e.g., aluminum, to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given silicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Although most frequently encountered in aluminosilicate form, many zeolites are known in silicate and borosilicate forms. For example, silicalite is a silicate form of ZSM-5 and is disclosed in U.S. Pat. No. 4,061,724, whereas AMS-1B is a borosilicate form of ZSM-5 and is disclosed in U.S. Pat. No. 4,269,813. It is also known to produce zeolite structures in which part or all of the silicon is replaced by other tetravalent elements, such as tin, titanium and/or germanium.
Many zeolites are synthesized in the presence of an organic directing agent, such as an organic nitrogen compound. For example, ZSM-5 may be synthesized in the presence of tetrapropylammonium cations and zeolite MCM-22 may be synthesized in the presence of hexamethyleneimine.
It is also known to use fluoride-containing compounds, such as hydrogen fluoride, as mineralizing agents in zeolite synthesis. For example, EP-A-337,479 discloses the use of hydrogen fluoride in water at low pH to mineralize silica in glass for the synthesis of ZSM-5.
One known zeolite is zeolite beta, the structure and synthesis of which in the presence of tetraethylammonium cations is disclosed in U.S. Pat. No. 3,308,069, the entire contents of which are incorporated herein by reference. As conventionally synthesized, zeolite beta is a highly faulted intergrowth of two polymorphs, A and B, which are normally found in a 60:40 ratio. However, the existence of a third polymorph, polymorph C, has also been proposed but to date this material has not been detected experimentally.
According to the present invention, a zeolite material, designated EMM-1, has been synthesized, which appears to have the hypothetical structure of the polymorph C of zeolite beta, by crystallizing a synthesis mixture which contains silica, germania, fluoride ions and an organonitrogen-directing agent.
The present invention is directed to a novel porous crystalline material, EMM-1, having the unit cell structure defined in Table 1 below and having, in its calcined form, an X-ray diffraction pattern including values substantially as set forth in Table 2 below.
The invention further resides in a method for preparing EMM-1 and in the conversion of organic compounds contacted with an active form of EMM-1.